On Fri, May 26, 2017 at 10:02:32PM +0200, Kevin Wolf wrote: > Am 26.05.2017 um 18:55 hat John Snow geschrieben: > > On 05/26/2017 07:40 AM, Kevin Wolf wrote: > > > There is one completely crazy thing that Xen does with respect to disks. > > > Instead of having support for their PV disks (i.e. virtio-blk, just > > > different) in the BIOS, they add _both_ an IDE disk and a PV disk to the > > > VM, so that the bootloader or non-PV-aware guest OSes can access the IDE > > > disk, for which they most certainly do have drivers. As soon as a driver > > > for the PV disk is loaded, however, that driver calls a hypervisor > > > function that removes all the IDE disks from the VM and leaves only the
Not hypervisor. It calls the PCI device which is emulated in QEMU. That "unplugs" the IDE. > > > PV ones there, so that the PV-aware guest doesn't see two same disks. > > > > > > I suspect that what you're seeing initially is the IDE disks, and when > > > the PV driver is loaded, they disappear. > > > > Sure, but does that mean that you'd see *no* block devices via a query > > afterwards? > > I believe xen_disk creates an anonymous BlockBackend, so it wouldn't > appear in 'info block'. Though remembering that Xen does weird things is > enough for me, I don't really want to know all the details that I am > lucky enough to have forgotten. And trust me, neither do you. Keep in mind that PV drivers are kernel drivers. Unless the qdisk driver is used - and then you should see that as well. > > Kevin >
